1. Field of the Invention
The present invention relates to an antenna apparatus utilizing an aperture of transmission line, and in particular, to an antenna apparatus which can be used in frequency bands such as bands of microwaves, quasi millimeter waves, millimeter waves, or the like.
2. Description of the Related Art
An antenna has been always used in wireless communication systems such as portable telephones. The concept of the conventional antenna has such a structure for resonating at a specified frequency, and a typical dipole antenna resonates at a half of an operating wavelength thereof.
In the dipole antenna, electromagnetic waves having the TM (Transverse Magnetic) mode are generated concentrically around the pole. However, electromagnetic waves that have reached a distance several times the wavelength interfere with one another at the boundary portions thereof, and the electromagnetic wave mode is transformed into TEM (Transverse Electro-Magnetic) mode (the radio waves thereof is called as transverse waves), and is radiated almost in a form of spherical waves. When the radius of curvature is increased, the electromagnetic waves become plane waves. The electromagnetic waves travel as group waves where a lots of electromagnetic waves travel so as to be distributed in a transverse straight line (namely, distributed averagely to a plane perpendicular to the traveling direction) concurrently travel. The documents which are related to the present invention are as follows:    Patent Document 1: Japanese patent laid-open publication No. JP 2005-244733 A;    Non-Patent Document 1: Kanji Otsuka, et al, “Measurement Potential Swing by Electric Field on Package Transmission Lines”, Proceedings of ICEP, pp. 490-495, April 2001;    Non-Patent Document 2: Kanji Otsuka, et al, “Measurement Evidence of Mirror Potential Traveling on Transmission Lines”, Technical Digest of 5th VLSI Packaging Workshop of Japan, pp. 27-28, December 2000; and    Non-Patent Document 3: Kanji Otsuka et al, “Stacked pair line”, Journal of Japan Institute of Electronics Packaging (JIEP), Vol. 4, No. 7, pp. 556-561, November, 2001.
Since the group waves fill up the space, the group waves need not only frequency allocation by the Radio Law but also a sufficient protection circuit against resonant mode noises leaking from the band, and the high-frequency circuit substantially becomes a circuit having a large overhead. Furthermore, the group waves are heavily attenuated even in the air at high frequencies in the bands equal to or higher than GHz band and become a level, that is larger than such an attenuation theorem at lower frequencies that the energy becomes weak in inverse proportion to the square of the distance (because of expansion in a spherical shape), and that is in inverse proportion to the cube of the distance by approximation, and this leads to that it is difficult to perform long distance communications.